After losing the first game to Andrea Petkovic of Germany in Grand Slam singles play, and trailing 30-0 in the second, Williams stretched to her right to return a serve, hit the ball and then yelped in pain, clutching toward her stomach.

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Afterward, Williams said the injury was in her "psoas" muscle, which flexes the hip and spinal column.

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"The last 48 hours, I just did as much pain management as I could," she said. "A lot of times when you play, you get that adrenalin and that blocks pain. I just didn't get enough of that today. I was hoping for some magic that I could recover."

Williams' younger sister, defending champion Serena Williams, didn't even make it to the tourney because of a foot injury.